This research mainly involves the analysis of long-term serial data (0-45 years) concerning subcutaneous fat thickness in human beings. Most of the data have been collected in major growth studies that will cooperate in this work. These data will be supplemented by others obtained from follow-up examinations (Berkeley, Fels, Harvard) and the range of data extended (fat biopsy studies--Fels, Harvard; underwater-weighing and caloric balance--Fels). The fat biopsy data will provide fat cell size. The underwater weight will allow the calculation of fat cell number (if cell size is known, and total body fat. This independent measure of total body fat will alllow an assessment of the validity of indirect measures, such as those based on weight and height. Blood triglycerides and cholesterol and the results of cardiovascular screening will be used to estimate the health significance of different levels and patterns of body fat. The major objectives are to establish the "normal" pattern of fat deposition and loss for the age range 0-45 years and, in addition: 1. to determine the importance of obesity as a predictor of subsequent obesity and subsequent disease. 2. to determine the causation (familial, genetic, etc.) and significance (illness experience) of obesity in infancy and at other ages. 3. to analyze the relationships between fat thickness and rate of maturation. 4. to determine the predictors of obesity in childhood, pubescence, early adulthood or middle age.